适用于QuickSort的Python程序

像合并排序一样，QuickSort是一种分而治之算法。它选择一个元素作为枢轴，并围绕拾取的枢轴对给定的数组进行分区。 quickSort有许多不同的版本，它们以不同的方式选择枢轴。

1. 始终选择第一个元素作为枢轴。
2. 始终选择最后一个元素作为枢轴(在下面实现)
3. 选择一个随机元素作为枢轴。
4. 选择中位数作为枢轴。

quickSort中的关键过程是partition()。分区的目标是，给定一个数组和一个数组元素x作为枢轴，将x放在排序数组中的正确位置，并将所有较小的元素(小于x)放在x之前，并将所有较大的元素(大于x)放在之后X。所有这些都应在线性时间内完成。
递归QuickSort函数的伪代码：

/* low  --> Starting index,  high  --> Ending index */
quickSort(arr[], low, high)
{
    if (low < high)
    {
        /* pi is partitioning index, arr[p] is now
           at right place */
        pi = partition(arr, low, high);

        quickSort(arr, low, pi - 1);  // Before pi
        quickSort(arr, pi + 1, high); // After pi
    }
}

Python

# Python program for implementation of Quicksort Sort
  
# This function takes last element as pivot, places
# the pivot element at its correct position in sorted
# array, and places all smaller (smaller than pivot)
# to left of pivot and all greater elements to right
# of pivot
  
  
def partition(arr, low, high):
    i = (low-1)         # index of smaller element
    pivot = arr[high]     # pivot
  
    for j in range(low, high):
  
        # If current element is smaller than or
        # equal to pivot
        if arr[j] <= pivot:
  
            # increment index of smaller element
            i = i+1
            arr[i], arr[j] = arr[j], arr[i]
  
    arr[i+1], arr[high] = arr[high], arr[i+1]
    return (i+1)
  
# The main function that implements QuickSort
# arr[] --> Array to be sorted,
# low  --> Starting index,
# high  --> Ending index
  
# Function to do Quick sort
  
  
def quickSort(arr, low, high):
    if len(arr) == 1:
        return arr
    if low < high:
  
        # pi is partitioning index, arr[p] is now
        # at right place
        pi = partition(arr, low, high)
  
        # Separately sort elements before
        # partition and after partition
        quickSort(arr, low, pi-1)
        quickSort(arr, pi+1, high)
  
  
# Driver code to test above
arr = [10, 7, 8, 9, 1, 5]
n = len(arr)
quickSort(arr, 0, n-1)
print("Sorted array is:")
for i in range(n):
    print("%d" % arr[i]),
  
# This code is contributed by Mohit Kumra
#This code in improved by https://github.com/anushkrishnav

请参阅有关QuickSort的完整文章以了解更多详细信息！